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Buck converter MPPT problem

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Newbie level 6
Nov 30, 2009
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Below attached my design for buck MPPT
All of the port will connect to pin header and to the microcontroller board. This buck is supplied from DC power supply of 18V to step down to 12V battery voltage. I wish to test this buck converter board individually without connecting to the MCU board. I am giving PWM to IR2104 driver at pin 2 using function generator. However I fail to turn on my NMOS because there is no output at IR2104. After sometime the R7 of 100 Ohm resistor at current sense burned. Is there any problem with the current sense circuit ?

1. Is my way of testing correct?
2. Is my design for buck converter works for MPPT application ?

Thank you


  • buck.pdf
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A buck converter operates by sending pulses of current through a coil. This can generate hi voltage spikes. It can ruin nearby mosfets unless you add safeguards.

You said R7 burns up. If so then it means extreme current is going through it. Furthermore this suggests IC LT6106 has fused innards.

Or on the other hand... it looks like R3 ( 0.1 ohm) is a current sense resistor. Is that the one that burns up? You could probably get by with a lower resistance that would dissipate fewer watts and stay cooler. Use the minimum ohms that will still create enough voltage drop across it to detect.

First you must stop the extreme current from going through it. At this point it may be that your mosfets are shorting at the same time. Check that they're still good.

in the schematics why do you need Q2 and D1 together?
Is Q2 is put to make the buck synchronous?

I dont see any reason for the R7 to blow.Because it should consume only the programmed current idealy since it is connected to the inverting terminal of the op-amp.

else everything looks ok.

First thing I would check is just the gate drive signals of the MOSFETs to make sure they have good break before make - the gate signals are not overlapping. This should be done without connecting the inductor or the current sense circuit.
When you give the signal to IR2104 from the function generator make sure the duty cycle is proper for 18 to 12V step down. Also since you put a function generator directly there is no soft start and since the inductor has to charge the big output cap with your fixed duty cycle provided by the function generator the current will overshoot in the beginning. This may cause excessive dissipation in the sense circuit.
I would also test the sense circuit separately to make sure the IC is still functional. Another thing to look at is how does your output voltage change?

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